Method for switching connections between stations of a group of stations from a first to a second satellite and associated group of stations

Description

[0001] The present invention relates to a method of changing connections between stations of a station group.

[0002] The invention further relates to a station group comprising several stations.

[0003] The invention relates to the field of satellite communications, in particular communications between several stations forming a group via satellites which are mobile relative to a geographical area.

[0004] Mobile satellites are satellites in non-geostationary orbit, for example in medium Earth orbit (MEO) or low Earth orbit (LEO). Mobile satellites can be used as communications relays for communications between stations located in a given geographical area for a predefined duration and at a predefined time. This duration and time are predefined by the ephemeris.

[0005] Before the mobile satellite disappears over the horizon, i.e. before this satellite becomes inaccessible for communication between the stations of the group via this satellite, it is necessary to switch the communication of the stations to another mobile satellite in order to ensure continuity of service. CN 112 822 738 A and US 2021 / 368407 A1 describe a method for changing station connections from one satellite to another.CN 112 822 738 A particularly describes a handover management method for a low-orbit satellite communication system in a dense user scenario, said method comprises the following steps: S1: grouping attribute prediction; a user terminal continuously measures the strength of the pilot signal transmitted by the satellite, and when the grouping operation is triggered, the user terminal performs grouping attribute prediction; S2: Member selection; the first satellite selects a user group at the edge of the handover at the time of triggering the handover, i.e., members of the same group according to the grouping attributes; S3: Preparation for group handover.The first satellite and the target satellite perform admission control, wireless resource reservation and channel allocation through "Group Handover Init" and "Group Handover Back" messages; S4: Handover execution, the first satellite sends a handover command to the user terminal to execute the handover.

[0006] In the context of communications within a group of stations, it is particularly important to coordinate the switchover from one satellite to another for all the stations in the group, since the absence of switchover of one or more stations in the group breaks the unity of the communication group. This is likely to result in the loss of communication, temporary or permanent, between the stations in the group. Also, the present invention aims to avoid this drawback by allowing continuity of communications between the members of the group, including when they are present under a constellation of satellites involving a periodic change of satellite acting as a relay.

[0007] To coordinate the switchover of the station group, a dedicated switchover orchestrator, also called a hub, is typically predefined. The predefined orchestrator is typically located at a fixed position on the ground and sends switchover commands.

[0008] However, in some cases it is complicated or even impossible to position the predefined orchestrator in the geographical area, for example given geographical constraints, for example in maritime areas far from the coasts.

[0009] Furthermore, during unavailability or failure of the predefined orchestrator, failover is not implemented. Therefore, communication between the stations in the group is likely to be interrupted when the moving satellite disappears over the horizon and thus becomes inaccessible for communication.

[0010] Finally, for example, when adding stations to the group, it is necessary to reconfigure the predefined orchestrator to also control the failover of this station, making this solution complicated and inflexible.

[0011] One aim of the invention is thus at least to reduce the aforementioned drawbacks.

[0012] In particular, the invention aims to obtain a method for changing connections of a group comprising several stations which is more reliable and / or more flexible.

[0013] To this end, the invention relates to a method for changing connections between stations of a group of stations, between a first state, in which each station of the group of stations is connected to a first satellite of a plurality of satellites, and a second state, in which each station of the group of stations is connected to a second satellite of the plurality of satellites, distinct from the first satellite, during the initialization of the change method, the stations being in the first state, each satellite being mobile relative to a geographical area in which the stations of said group of stations are positioned, each station being able to establish a connection with each satellite during a predetermined duration of presence of said satellite, considered for said geographical area, the change method comprising: a phase of electing at least one station from among the stations of the group of stations, based on at least one characteristic relating to a satellite antenna of said station, to obtain at least one elected station, the or each elected station being a station which commands a switch between the first state and the second state; a switchover phase, comprising a step of broadcasting, by the or each elected station to the other stations of the group of stations, an instruction to switch the connection from the first satellite to the second satellite.

[0014] In fact, the change process allows for a switch of the station group between a first and a second satellite which is more flexible and / or reliable.

[0015] By electing the station(s) configured to control the switchover according to the invention, the characteristic(s) of the antenna is / are taken into account, such as a switchover capability. Therefore, the station(s) are elected based on their ability to form an orchestrator for the change of connections between the first and second satellites.

[0016] This allows for a reliable switchover. Indeed, one or more of the stations can act as an orchestrator for the switchover according to the invention.

[0017] Even when one of the stations in the group is lost or unavailable, the switchover is implemented by another station elected for this purpose.

[0018] In particular, the switching process allows for a switchover to be achieved in the absence of a predefined orchestrator. Thus, the switchover function is implemented by the elected station(s) of the group itself.

[0019] According to other advantageous aspects of the invention, the changing method comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations: the characteristic relating to the satellite antenna of the station comprises a switching time between the connection to the first satellite and the connection to the second satellite of said station and / or comprises a capacity for establishing connections simultaneously with the first satellite and the second satellite by said station; the election phase comprises the election of the or each elected station furthermore according to a calculation capacity of said station, preferably the calculation capacity comprising a capacity to estimate a transit time of a signal transmitted via the second satellite and / or a capacity to estimate the Doppler effect of the signal transmitted via the second satellite; the election phase comprises: a first step of determining, by each station, a marking assigned to this station, from among a plurality of predetermined markings, according to the characteristic relating to the satellite antenna of said station; a second step of determining,wherein each station determines, at least based on the marking at that station, an eligibility to form an elected station of the elected station(s); each station determines the marking assigned to that station from among: a first marking, called preferential marking, when the satellite antenna of said station is configured to simultaneously establish a connection with the first satellite and the second satellite; a second marking, called secondary marking, when the satellite antenna of said station is configured to establish a connection, at a given time, only with one of the first satellite and the second satellite, and when the satellite antenna further has a switching duration of the connection between the first satellite and the second satellite less than or equal to a predetermined threshold; a third marking, called unsuitable marking, when the satellite antenna of said station is configured to establish a connection,at a given time, only with one of the first satellite and the second satellite, and when the satellite antenna further has a switching duration of the connection between the first satellite and the second satellite strictly greater than the predetermined threshold; the election phase further comprises a step of reception, by one of the stations of the group of stations, called the station in question, of a message comprising the marking of one of the stations of the group of stations other than the station in question, called the other station, and in which, during the second determination step, the station in question determines its eligibility to form an elected station of the elected station(s) furthermore according to said message; during the second determination step,the station in question determines its eligibility according to at least one of the following criteria: if the marking of the station in question is the secondary marking and the message includes the preferential marking of the other station, the station in question determines that it is not eligible to form an elected station of the elected station(s), if the marking of the station in question is the secondary marking and the message includes the secondary marking of the other station, the station in question determines that it is eligible to form an elected station of the elected station(s) only if the switching duration is among the N stations having the shortest switching duration among the switching durations of all the stations in the group of stations, N being a predetermined integer, if the marking of the station in question is the preferential marking,the station in question determines that it is eligible to form an elected station of the elected station(s), preferably independently of the message; the switchover phase comprises a step of planning a switchover time between the connection to the first satellite and the connection to the second satellite for each station, based on the ephemerides of at least the first and second satellites, and in which the switchover instruction comprises the switchover time; the switchover phase comprises a step of verifying a presence of the second satellite, during which the or each elected station transmits a beacon signal to the second satellite, and receives a response to the beacon signal from the second satellite when said second satellite is present, preferably, the broadcasting step being implemented only upon receipt of said response; during the broadcasting step,the elected station(s) broadcasts the switchover instruction via the first satellite to the other stations in the station group.

[0020] The present invention also relates to a group of stations comprising several stations configured to change connections between the stations, between a first state, in which each station of the group of stations is connected to a first satellite of a plurality of satellites, and a second state, in which each station of the group of stations is connected to a second satellite of the plurality of satellites, distinct from the first satellite, each satellite being mobile relative to a geographical area in which the stations of said group of stations are positioned, each station being able to establish a connection with each satellite during a predetermined duration of presence of said satellite, considered for said geographical area, the group of stations being configured to elect at least one station from among the stations of the group of stations, as a function of at least one characteristic relating to a satellite antenna of said station,to obtain at least one elected station, the or each elected station being configured to command a switch between the first state and the second state, the or each elected station being configured to broadcast, to the other stations of the group of stations, an instruction to switch the connection from the first satellite to the second satellite.,

[0021] These characteristics and advantages of the invention will appear on reading the description which follows, given solely as a non-limiting example, and made with reference to the appended drawings, in which: there figure 1is a schematic view of a communication system comprising a group of stations according to the invention and a constellation of satellites, of which only a first satellite of the constellation, accessible for communication with the stations, is represented, the communication system being in a first state, in which each station is connected to the first satellite; the figure 2 is a schematic view of the communication system of the figure 1 , in which the first satellite and a second satellite of the constellation, accessible for communication, are represented, the communication system being in an intermediate failover state; the figure 3 is a schematic view of the communication system of figures 1 And 2, in which only the second satellite of the constellation, accessible for communication, is represented, the communication system being in a second state, in which each station is connected to the second satellite, and the first satellite is in particular inaccessible; and the figure 4 is a flowchart of a change method according to the invention, implemented by the group of stations of the communication system of the figures 1 has 3 .

[0022] In reference to the figures 1 to 3 , a communication system 10 comprises a constellation 12 of satellites and a group of stations 14 comprising several stations 16-1, 16-2, 16-3 configured to communicate with each other using the constellation 12 of satellites.

[0023] The constellation 12 comprises N satellites 20-1 to 20-N mobile relative to a geographic area in which the stations 16-1, 16-2, 16-3 of the group of stations 14 are positioned. The number N is greater than 2, advantageously greater than 10 and preferably greater than 50. Generally, the number N can be between 2 and 1000. In certain embodiments, the number N is between 2 and 10,000. Still in certain other embodiments, the number N is greater than 10,000.

[0024] A "mobile satellite" is understood to mean, in particular, a satellite moving in a non-geostationary orbit, such as low Earth orbit or medium Earth orbit. figures 1 to 3 , examples of satellite movement are illustrated by arrows 21.

[0025] In the examples of the figures 1 to 3, only satellites 20-1 to 20-N accessible to station group 14 for communication are shown. For example, in the figure 1 , only a first satellite 20-1 of the constellation 12 is represented, in the figure 2 , the first satellite and a second satellite 20-2 of the constellation 12 are represented, and in the figure 3 , only the second satellite 20-2 is represented.

[0026] Each satellite 20-1 to 20-N forms in particular a communications relay between all the stations 16-1, 16-2, 16-3 of the group of stations 14, all notably located in the geographical area, and this in particular for a predefined duration and at a predefined time. This duration and this time are predefined by the ephemerides.

[0027] Each satellite 20-1 to 20-N includes a payload 22 comprising all of its electronic components enabling it to ensure its communication functions with the group of stations 14 and optionally with the other satellites.

[0028] The payloads 22 of satellites 20-1 to 20-N are, for example, substantially similar to each other.

[0029] For example, each payload 22 comprises, not shown, a radiofrequency signal receiver / transmitter configured to receive and transmit radiofrequency signals comprising the communications of the group of stations 14. Each payload 22 further comprises, for example, at least one control and command circuit for the transmitter / receiver. The transmitter / receiver defines at least one spot 24, in which communication between the groups of stations 14 via the corresponding satellite 20-1 to 20-N is implemented. In particular, no communication between the group of stations 14 positioned outside the spot 24 and the corresponding satellite 20-1 to 20-N is possible.

[0030] Station group 14 includes M stations 16-1 to 16-M. The number M is greater than 2. According to the example of figures 1 to 3 , station group 14 includes three stations 16-1, 16-2, 16-3.

[0031] Each station 16-1 to 16-M of group 14 is configured to communicate, via one of the satellites 20-1 to 20-N with the other stations 16-1 to 16-M of group 14.

[0032] Each station 16-1 to 16-M is a ground station. By "ground station" is meant in particular a station positioned on the surface of the Earth or in the atmosphere. In particular, the ground station is distinct from a station on board a satellite.

[0033] Each station 16-1 to 16-M is for example a fixed ground station, or a mobile station.

[0034] When station 16-1 to 16-M is a mobile station, it is preferably mobile within the geographic area. For example, the mobile station is on board a land vehicle, a marine vehicle, or an aircraft.

[0035] Each station 16-1 to 16-M comprises at least one control module 30, a satellite transmitter / receiver 32 and at least one satellite antenna 34, 36 connected to the satellite transmitter / receiver 32 for establishing communications with the other stations 16-1 to 16-M of the group 14 via the intermediary of the satellite 20-1 to 20-N.

[0036] The control module 30 comprises a memory and a processor, not shown. The control module 30 is in particular configured to determine messages of the communication implemented between the stations 16-1 to 16-M via the satellite transmitter / receiver 32 and the satellite antenna 34, 36.

[0037] The satellite transceiver 32 comprises, for example, a modem. The satellite transceiver 32 is in particular configured to convert digital signals from the control module 30 into analog signals for transmission via the satellite antenna 34, 36 to the satellite(s) 20-1 to 20-N. The satellite transceiver 32 is further configured to convert analog signals received by the satellite antenna 34, 36 into digital signals and transmit them to the control module 30.

[0038] According to one example, the satellite transceiver 32 is configured to simultaneously convert digital signals into analog signals for transmitting signals simultaneously to two of the satellites 20-1 to 20-N simultaneously. Also, the satellite transceiver 32 is for example configured to simultaneously convert analog signals received from the two satellites into digital signals.

[0039] Analog signals are specifically radio frequency signals. For example, radio frequency signals are signals in one or more bands allocated to satellite communications, such as the C, X, Ku, Ka bands, etc.

[0040] The satellite antenna is preferably either a satellite antenna 34 of the type called multiple pointing, or a satellite antenna 36 of the type called single pointing in the present description.

[0041] The multi-pointing type satellite antenna 34 is configured to establish connections simultaneously with at least two satellites among the satellites 20-1 to 20-N, positioned in distinct directions relative to the satellite antenna 34.

[0042] Preferably, the multiple pointing type satellite antenna 34 is an electronic antenna, in particular without moving mechanical parts for reorientation of the antenna.

[0043] The single-pointing satellite antenna 36 is configured to establish, at a given instant, a connection with only one of the satellites 20-1 to 20-N. In particular, the single-pointing satellite antenna 36 is configured to implement a connection in a single direction, at a given instant.

[0044] The single-pointing type satellite antenna 36 is in particular unable to implement a connection simultaneously with two or more satellites 20-1 to 20-N, positioned in different directions relative to this antenna.

[0045] The single-pointing type satellite antenna 36 is preferably a parabolic antenna. For example, the satellite antenna 36 is configured to be rotated in the direction of the given satellite 20-1 to 20-N to establish the connection.

[0046] According to another example, the simple pointing type satellite antenna 36 is an electronic antenna, in particular without moving mechanical parts for reorientation of the antenna, but capable of establishing, at a given moment, a connection in a single direction with one of the satellites 20-1 to 20-N.

[0047] Preferably, at least one of the stations 16-1 to 16-M of the group comprises the satellite antenna 34 of the multiple pointing type and at least one of the stations 16-1 to 16-M of the group comprises the satellite antenna 36 of the single pointing type.

[0048] For example, with reference to the figures 1 to 3 , station 16-1 includes the multi-pointing type satellite antenna 34, and stations 16-2 and 16-3 include the single-pointing type satellite antenna 36. Each satellite antenna 36 is configured to be rotationally oriented to the corresponding satellite 20-1 to 20-N, as illustrated by arrows 38.

[0049] A change method 100 implemented by the communication system 10, and in particular by the stations 16-1 to 16-M of the station group 14, is now explained with reference to the figure 4 presenting a flowchart of the steps in this process.

[0050] It is considered that during the implementation of this process, satellites 20-1 to 20-N are moving along their usual orbit.

[0051] When scrolling through satellites 20-1 to 20-N, each satellite is accessible for communication with stations 16-1 to 16-M positioned in spot 24 at a predefined time and for a predefined duration.

[0052] The changing method 100 comprises changing the connections of all stations 16-1 to 16-M of the station group 14 between a first state and a second state.

[0053] In the first state, an example of which is illustrated in the figure 1, each station 16-1 to 16-M of the station group 14 is connected to the same satellite, for example to the first satellite 20-1. Preferably, each station 16-1 to 16-M is not connected to satellites other than the first satellite 20-1 during the initialization of the change method 100. In the second state, an example of which is illustrated in the figure 3 , each station 16-1 to 16-M of the station group 14 is connected to a satellite distinct from the first satellite 20-1, namely the second satellite 20-2. In other words, in the first state, all stations 16-1 to 16-M of the station group 14 are connected to the first satellite 20-1, and in the second state, all stations 16-1 to 16-M are connected to the second satellite 20-2.

[0054] When initializing the change method 100, the communication system 10 is in the first state.

[0055] The switching process 100 comprises an election phase 110 and a switchover phase 120.

[0056] In the election phase 110, at least one station among the plurality of stations 16-1 to 16-M of the station group 14 is elected to control a switch between the first state and the second state. The station(s), which are elected in the election phase 110, are called elected station(s).

[0057] The election of the elected station(s) depends on at least one characteristic relating to the satellite antenna 34, 36 of the respective elected station. Examples of the characteristic(s) are described below.

[0058] The election phase 110 comprises for example a first determination step 130, a reception step 135 and a second determination step 140.

[0059] During the first determination step 130, each station 16-1 to 16-M determines a marking assigned to the station, from among a plurality of predetermined markings, at least as a function of the characteristic relating to the satellite antenna 34, 36 of the station 16-1 to 16-M.

[0060] The characteristic relating to the satellite antenna 34, 36 of the elected station comprises for example a switching time between the connection to the first satellite 20-1 and the connection to the second satellite 20-2. For example, when the satellite antenna 36 is of the simple pointing type and the reorientation of the antenna is implemented by rotation of the antenna, the switching time corresponds to the time for the reorientation of the satellite antenna 36 between the satellites 20-1 and 20-2.

[0061] According to another example or as an optional addition, the characteristic comprises a capacity for establishing connections simultaneously with the first satellite 20-1 and the second satellite 20-2. For example, when the satellite antenna 34 is of the multiple pointing type, this antenna has the capacity for establishing connections simultaneously with the first satellite 20-1 and the second satellite 20-2.

[0062] During the first determination step 130, the or each station 16-1 to 16-M determines the marking and assigns this marking to itself, for example, from among a first marking, called preferential marking, a second marking, called secondary marking, and a third marking, called unsuitable marking.

[0063] The or each station 16-1 to 16-M determines and assigns itself the preferential marking, when the satellite antenna 34 of the station 16-1 to 16-M is configured to simultaneously establish a connection with the first satellite 20-1 and the second satellite 20-2. In particular, in this case, the satellite antenna 34 is of the multiple pointing type.

[0064] When station 16-1 to 16-M assigns itself the preferential marking, it considers itself the preferred station to control the switch between the first state and the second state.

[0065] The or each station 16-1 to 16-M determines and assigns itself the secondary marking, when the satellite antenna 36 of the station 16-1 to 16-M is of the simple pointing type and the switching duration of the connection between the first satellite 20-1 and the second satellite 20-2 is furthermore less than or equal to a predetermined threshold. In other words, the satellite antenna 36 is configured to establish a connection, at a given instant, only with one of the first satellite 20-1 and the second satellite 20-2, that is to say is of the simple pointing type, and furthermore has the switching duration greater than the predetermined threshold.

[0066] The predetermined threshold is in particular chosen so as to guarantee a switchover of the connections of all the stations 16-1 to 16-M from the first satellite 20-1 to the second satellite 20-2 during the switchover phase 120 before the disappearance of the first satellite 20-1 on the horizon, as described in the context of the description of the switchover phase 120.

[0067] When station 16-1 to 16-M assigns itself the secondary marking, it considers itself as a station which is capable of controlling the switch between the first state and the second state, but which is less suitable than each station presenting the preferential marking.

[0068] The or each station 16-1 to 16-M determines and assigns itself the unfit marking, when the satellite antenna 36 of the station 16-1 to 16-M is of the simple pointing type and when the antenna also has a switching duration of the connection between the first satellite and the second satellite strictly greater than the predetermined threshold. In this case, the station 16-1 to 16-M considers itself in particular as unfit to control the switchover.

[0069] According to an example, each station 16-1 to 16-M further determines its marking based on a computing capacity of station 16-1 to 16-M.

[0070] For example, the computational capability includes, or is defined by, the capability to estimate the Doppler shift of a signal transmitted between station 16-1 to 16-M and the first or second satellite 20-1, 20-2.

[0071] Additionally or alternatively, the computing capability includes, or is defined by, the capability of the station 16-1 to 16-M to determine a transit time of a signal transmitted via the first or via the second satellite 20-1, 20-2, for example of a beacon signal.

[0072] The expression "transit time" means in particular the duration between the time of transmission, by station 16-1 to 16-M, of the signal to the corresponding satellite, and the time of reception, by the same station 16-1 to 16-M, of a response from this satellite following the transmission of the signal.

[0073] When the corresponding station 16-1 to 16-M has the computing capacity to estimate the Doppler effect and / or the signal transit time, it assigns itself, for example, the preferential marking.

[0074] Information including the estimation of the Doppler effect and / or the transit time makes it possible in particular to establish a connection with the second satellite 20-2 very quickly during the switchover phase 120, since the station 16-1 to 16-M switching the connection from the first satellite 20-1 to the second satellite 20-2 is capable of finding the second satellite 20-2 quickly, and thus establishing the connection.

[0075] According to one example, each station 16-1 to 16-M further determines its marking based on the transit time of the signal transmitted via the first or second satellite 20-1, 20-2, for example by sending and receiving a beacon signal via the corresponding satellite.

[0076] Preferably, the or each station 16-1 to 16-M assigning itself the respective marking, transmits to the other stations 16-1 to 16-M a message comprising an identifier of the station 16-1 to 16-M and this marking.

[0077] In the receiving step 135, at least one of the stations 16-1 to 16-M, preferably each station 16-1 to 16-M of the group 14, receives the message comprising the marking of another station 16-1 to 16-M of the group 14. The or each station 16-1 to 16-M receiving the message is called "station considered" in the present description.

[0078] During the second determination step 140, each station determines, at least based on its marking, an eligibility to form the elected station. Preferably, the station considered 16-1 to 16-M determines its eligibility to form the elected station further based on the message received during the reception step 135.

[0079] For example, during the second determination step 140, the station considered 16-1 to 16-M determines its eligibility to form the elected station according to at least one criterion among a first criterion, a second criterion and a third criterion, preferably according to all of these criteria.

[0080] According to the first criterion, the station considered 16-1 to 16-M determines that it is not eligible to form the elected station, if its marking is the secondary marking and the message received from the other station during step 135 includes the preferential marking of the other station.

[0081] According to the second criterion, the considered station 16-1 to 16-M determines that it is eligible to form the elected station, if its marking is the secondary marking and if, in addition, the switching duration is part of the N stations 16-1 to 16-M having the shortest switching duration among the switching durations of all the stations 16-1 to 16-M of the station group 14. N is a predetermined integer, and is for example equal to 2 or 3.

[0082] According to the third criterion, the station considered determines that it is eligible to form the elected station, if the marking of the station considered is the preferential marking. In this case, the station considered preferably determines that it is eligible independently of the message. According to an example, in this case, the station considered determines that it is eligible only if a number of other stations of the group of stations 14 considered as eligible, is less than a predetermined number. This makes it possible in particular to limit the number of stations of the group of stations 14 determining that they are eligible to form the elected station.

[0083] The switchover phase 120 comprises the switchover of all the connections of the stations 16-1 to 16-M from the first satellite 20-1, i.e. from the first state, to the second satellite 20-2, i.e. to the second state.

[0084] The switchover phase 120 is preferably implemented when the communication system 10 is in an intermediate switchover state, illustrated in figure 2 , wherein both the first and second satellites 20-1 and 20-2 are accessible for communication.

[0085] The switchover phase 120 comprises in particular a step 145 of planning a switchover time, a step 150 of verifying the presence of the second satellite 20-2, a step 155 of developing a switchover instruction, a step 160 of broadcasting this instruction and a step 165 of applying this instruction.

[0086] In the planning step 145, the elected station 16-1 to 16-M determines a switchover time between the connection to the first satellite 20-1 and the connection to the second satellite 20-2 for each station 16-1 to 16-M. The elected station 16-1 to 16-M determines the switchover time at least based on the ephemeris of the first and second satellites 20-1, 20-2.

[0087] In the verification step 150, the elected station 16-1 to 16-M verifies the presence of the second satellite 20-2. In particular, the elected station 16-1 to 16-M transmits a beacon signal to the second satellite 20-2, and receives a response to the beacon signal from the second satellite 20-2 when the second satellite 20-2 is present.

[0088] To do this, if the satellite antenna 34 of the elected station 16-1 to 16-M is of the multiple pointing type, the elected station 16-1 to 16-M transmits the beacon signal to the second satellite 20-2 and continues to be connected to the first satellite 20-1 simultaneously.

[0089] If the satellite antenna 36 of the elected station 16-1 to 16-M is of the simple pointing type, the elected station 16-1 to 16-M interrupts the connection with the first satellite 20-1, reorients the satellite antenna 36 to the second satellite 20-2, for example by rotating the satellite antenna 36, ​​and transmits the beacon signal to the second satellite 20-2. Upon receiving the response to the beacon signal, the elected station 16-1 to 16-M again rotates the satellite antenna 36 towards the first satellite 20-1, in particular before implementing the development step 155 and the broadcasting step 160.

[0090] In the elaboration step 155, the elected station 16-1 to 16-M elaborates the switchover instruction.

[0091] The switchover instruction comprises a command to switch the connection to the second satellite 20-2. The switchover instruction further comprises, for example, an identifier and time-dependent positions of the second satellite 20-2. Preferably, the switchover instruction further comprises the switchover time.

[0092] When the elected station 16-1 to 16-M has the capability to estimate the Doppler effect of a signal transmitted via the second satellite 20-2, the switchover instruction preferably includes an indication of the estimated Doppler effect for the transmission.

[0093] When the elected station 16-1 to 16-M has the capability to estimate the transit time of a signal transmitted via the second satellite 20-2, the handover instruction preferably includes this estimated transit time.

[0094] This allows in particular each station 16-1 to 16-M applying the switchover instruction during the application step 165, to establish the connection with the second satellite 20-2 very quickly, since this station knows certain parameters for establishing the connection, namely the Doppler effect and / or the estimated transit time.

[0095] In the broadcasting step 160, the elected station broadcasts the switchover instruction via the first satellite 20-1 to the other stations in the group. For example, the elected station broadcasts the switchover instruction several times, in particular periodically.

[0096] Preferably, the broadcasting step 160 is only implemented following the reception, during the verification step 150, by the elected station 16-1 to 16-M of the response to the beacon signal.

[0097] For example, the elected station broadcasts the switch instruction for a predetermined broadcast duration. Preferably, the elected station begins broadcasting at a given time before the switch time. A time interval between this given time and the switch time depends, for example, on the switching duration of the elected station. Preferably, the time interval is greater than the sum of the switching duration and the predetermined broadcast duration.

[0098] This allows in particular the elected station, in particular when it includes the simple pointing type satellite antenna 36, ​​to establish the connection with the second satellite 20-2 before the connection of the other stations 16-1 to 16-M to the second satellite 20-2, and thus to monitor the switchover of all the stations 16-1 to 16-M to the second satellite 20-2 during the application step 165.

[0099] In the application step 165, each station 16-1 to 16-M of the group 14 receives the switchover instruction, and applies the instruction, switching the connection from the first satellite 20-1 to the second satellite 20-2.

[0100] The planning 145, verification 150, development 155 and broadcasting 160 steps are implemented by the elected station 16-1 to 16-M, which is elected during the election phase 110. When several stations 16-1 to 16-M are elected, during the election phase 110, to form the elected stations, each of these stations preferably implements the steps 145, 150, 155 and 160.

[0101] For example, when several stations 16-1 to 16-M are the elected stations, each elected station broadcasts for example the switching instruction during the broadcasting step 160, and each station 16-1 to 16-M, in particular the stations other than the elected stations, applies, during the application step 165, the switching instruction received first.

[0102] Preferably, the election phase 110 is repeated several times before the implementation of the switchover phase 120.

[0103] Of course, other embodiments may be envisaged. For example, steps 130 to 155 and 165 are optional steps, and / or variants of these steps are conceivable, without however departing from the scope of the invention as defined by the claims.

Claims

1. A method for changing (100) connections between stations (16-1, 16-2, 16-3) of a group of stations (14) between a first state, wherein each station (16-1, 16-2, 16-3) of the group of stations (14) is connected to a first satellite (20-1) of a plurality of satellites (20-1, 20-2), and a second state, wherein each station (16-1, 16-2, 16-3) of the group of stations (14) is connected to a second satellite (20-2) of the plurality of satellites (20-1, 20-2), distinct from the first satellite (20-1), upon initialisation of the change method (100), the stations (16-1, 16-2, 16-3) being in the first state, each satellite (20-1, 20-2) being mobile relative to a geographical area wherein the stations (16-1, 16-2, 16-3) of said group of stations (14) are positioned, each station (16-1, 16-2, 16-3) being capable of establishing a connection with each satellite (20-1, 20-2) for a predetermined duration of presence of said satellite (20-1, 20-2), considered for said geographical area, characterised in that the change method (100) comprises: - an phase (110) of electing at least one station among the stations (16-1, 16-2, 16-3) of the group of stations (14), as a function of at least one characteristic relating to a satellite antenna (34, 36) of said station (16-1, 16-2, 16-3), in order to obtain at least one elected station, the or each elected station being a station which controls a changeover between the first state and the second state; - a changeover phase (120), comprising a step of broadcasting (160), by the or each elected station to the other stations (16-1, 16-2, 16-3) of the group of stations (14), an instruction to switch the connection from the first satellite (20-1) to the second satellite (20-2).

2. The change method (100) according to claim 1, wherein the characteristic relating to the satellite antenna (34, 36) of the station (16-1, 16-2, 16-3) comprises a switching duration for switching between the connection to the first satellite (20-1) and the connection to the second satellite (20-2) of said station (16-1, 16-2, 16-3) and / or comprises a capability of establishing connections simultaneously with the first satellite (20-1) and the second satellite (20-2) by said station (16-1, 16-2, 16-3).

3. The change method (100) according to claim 1 or 2, wherein the election phase (110) comprises electing the or each station elected additionally according to a computing capability of said station (16-1, 16-2, 16-3).

4. The change method (100) according to claim 3, wherein the computing capability comprises a capability to estimate a transit time of a signal transmitted via the second satellite (20-2) and / or a capability to estimate the Doppler effect of the signal transmitted via the second satellite (20-2).

5. The change method (100) according to any one of the preceding claims, wherein the election phase (110) comprises: - a first step (130) of determining, by each station (16-1, 16-2, 16-3), a marking assigned to this station, from among a plurality of predetermined markings, as a function of the characteristic relating to the satellite antenna (34, 36) of said station (16-1, 16-2, 16-3); - a second step (140) of determining, wherein each station (16-1, 16-2, 16-3) determines, at least as a function of the marking at that station, an eligibility to form an elected station of the elected station(s).

6. The change method (100) according to claim 5, wherein each station (16-1, 16-2, 16-3) determines the marking assigned to that station from: - a first marking, known as preferred marking, when the satellite antenna (34) of said station (16-1, 16-2, 16-3) is configured to simultaneously establish a connection with the first satellite (20-1) and the second satellite (20-2); - a second marking, referred to as secondary marking, when the satellite antenna (36) of said station is configured to establish a connection, at a given time, only with one of the first satellite (20-1) and the second satellite (20-2), and when the satellite antenna (36) also has a switching duration for the connection between the first satellite (20-1) and the second satellite (20-2) that is less than or equal to a predetermined threshold; - a third marking, referred to as unfit marking, when the satellite antenna (36) of said station is configured to establish a connection, at a given time, only with one of the first satellite (20-1) and the second satellite (20-2), and when the satellite antenna (36) also has a switching duration for the connection between the first satellite (20-1) and the second satellite (20-2) that is strictly greater than or equal to a predetermined threshold.

7. The change method (100) according to claim 5 or 6, wherein the election phase (110) further comprises a step of receiving (135), by one of the stations (16-1, 16-2, 16-3) of the group of stations (14), referred to as the station in question, a message comprising the marking of one of the stations (16-1, 16-2, 16-3) of the group of stations (14) other than the station in question, referred to as the other station, and wherein, during the second step of determining (140), the station in question determines its eligibility to form an elected station of the elected station(s) additionally as a function of said message.

8. The change method (100) according to claim 7, wherein, during the second step of determining (140), the station in question determines its eligibility according to at least one of the following criteria: - if the marking of the station in question is the secondary marking and the message includes the preferred marking of the other station, the station in question determines that it is not eligible to form an elected station of the elected station(s); - if the marking of the station in question is the secondary marking and the message comprises the secondary marking of the other station, the station in question determines that it is eligible to form an elected station of the elected station(s) only if the switching duration is one of the N stations (16-1, 16-2, 16-3) that has the shortest switching duration among the switching times of all the stations (16-1, 16-2, 16-3) of the group of stations (14), N being a predetermined integer, - if the marking of the station in question is the preferred marking, the station in question determines that it is eligible to form an elected station of the elected station(s).

9. The change method (100) according to claim 8, characterised in that if the marking of the station in question is the preferred marking, the station in question determines that it is eligible to form an elected station of the elected station(s) independently of the message.

10. The change method (100) according to any one of the preceding claims, wherein the changeover phase (120) comprises a step for scheduling (145) a changeover time for when to change between the connection to the first satellite (20-1) and the connection to the second satellite (20-2) for each station, as a function of the ephemerides of at least the first and second satellites (20-1, 20-2), and wherein the changeover instruction comprises the changeover time.

11. The change method (100) according to any one of the preceding claims, wherein the changeover phase (120) comprises a step of verifying (150) a presence of the second satellite (20-2), during which the or each elected station transmits a beacon signal to the second satellite (20-2), and receives a response to the beacon signal from the second satellite (20-2) when the said second satellite (20-2) is present.

12. The change method (100) according to claim 11, wherein the broadcasting step (160) is only implemented upon receipt of said response.

13. The change method (100) according to any one of the preceding claims, wherein, during the broadcasting step (160), the or each elected station broadcasts the changeover instruction via the first satellite (20-1) to the other stations (16-1, 16-2, 16-3) in the group of stations (14).

14. A group of stations (14) comprising a plurality of stations (16-1, 16-2, 16-3) configured to change connections between stations (16-1, 16-2, 16-3), between a first state, wherein each station (16-1, 16-2, 16-3) of the group of stations (14) is connected to a first satellite (20-1) of a plurality of satellites (20-1, 20-2), and a second state, wherein each station (16-1, 16-2, 16-3) of the group of stations (14) is connected to a second satellite (20-2) of the plurality of satellites (20-1, 20-2), distinct from the first satellite (20-1), each satellite (20-1, 20-2) being mobile relative to a geographical area wherein the stations (16-1, 16-2, 16-3) of said group of stations (14) are positioned, each station (16-1, 16-2, 16-3) being capable of establishing a connection with each satellite (20-1, 20-2) for a predetermined duration of presence of said satellite (20-1, 20-2), considered for said geographical area, characterised in that the group of stations (14) is configured to elect at least one station from among the stations (16-1, 16-2, 16-3) of the group of stations (14), as a function of at least one characteristic relating to a satellite antenna (34, 36) of said station (16-1, 16-2, 16-3), to obtain at least one elected station, the or each elected station being configured to control a changeover between the first state and the second state, and in that the or each elected station is configured to broadcast, to the other stations (16-1, 16-2, 16-3) of the group of stations (14), an instruction to switch the connection from the first satellite (20-1) to the second satellite (20-2).